Estudio sobre la producción de ácido láctico a partir de un proceso de fermentación de melaza

Tesis (Maestría en Ingeniería Química) UANLUANLhttp://www.uanl.mx

The Peripheral Stalk of Rotary ATPases

Rotary ATPases are a family of enzymes that are thought of as molecular nanomotors and are classified in three types: F, A, and V-type ATPases. Two members (F and A-type) can synthesize and hydrolyze ATP, depending on the energetic needs of the cell, while the V-type enzyme exhibits only a hydrolytic activity. The overall architecture of all these enzymes is conserved and three main sectors are distinguished: a catalytic core, a rotor and a stator or peripheral stalk. The peripheral stalks of the A and V-types are highly conserved in both structure and function, however, the F-type peripheral stalks have divergent structures. Furthermore, the peripheral stalk has other roles beyond its stator function, as evidenced by several biochemical and recent structural studies. This review describes the information regarding the organization of the peripheral stalk components of F, A, and V-ATPases, highlighting the key differences between the studied enzymes, as well as the different processes in which the structure is involved

Intersubunit ionic interactions stabilize the nucleoside diphosphate kinase of <i>Mycobacterium tuberculosis</i>

Most nucleoside diphosphate kinases (NDPKs) are hexamers. The C-terminal tail interacting with the neighboring subunits is crucial for hexamer stability. In the NDPK from Mycobacterium tuberculosis (Mt) this tail is missing. The quaternary structure of Mt-NDPK is essential for full enzymatic activity and for protein stability to thermal and chemical denaturation. We identified the intersubunit salt bridge Arg(80)-Asp(93) as essential for hexamer stability, compensating for the decreased intersubunit contact area. Breaking the salt bridge by the mutation D93N dramatically decreased protein thermal stability. The mutation also decreased stability to denaturation by urea and guanidinium. The D93N mutant was still hexameric and retained full activity. When exposed to low concentrations of urea it dissociated into folded monomers followed by unfolding while dissociation and unfolding of the wild type simultaneously occur at higher urea concentrations. The dissociation step was not observed in guanidine hydrochloride, suggesting that low concentration of salt may stabilize the hexamer. Indeed, guanidinium and many other salts stabilized the hexamer with a half maximum effect of about 0.1 M, increasing protein thermostability. The crystal structure of the D93N mutant has been solved

Advantage of terahertz radiation versus X-ray to detect hidden organic materials in sealed vessels

International audienceTerahertz imaging and conventional X-ray have been used to investigate a sealed Ancient Egyptian jar preserved at the Museum of Aquitaine (France). Terahertz radiation revealed an unknown content that could not have been visualized by X-ray. By comparison with a model object, we concluded that this content was composed of organic materials explaining their relative radiolucency

Molecular Basis of the Pathogenic Mechanism Induced by the m.9191T>C Mutation in Mitochondrial ATP6 Gene

International audienceProbing the pathogenicity and functional consequences of mitochondrial DNA (mtDNA) mutations from patient's cells and tissues is difficult due to genetic heteroplasmy (co-existence of wild type and mutated mtDNA in cells), occurrence of numerous mtDNA polymorphisms, and absence of methods for genetically transforming human mitochondria. Owing to its good fermenting capacity that enables survival to loss-of-function mtDNA mutations, its amenability to mitochondrial genome manipulation, and lack of heteroplasmy, Saccharomyces cerevisiae is an excellent model for studying and resolving the molecular bases of human diseases linked to mtDNA in a controlled genetic background. Using this model, we previously showed that a pathogenic mutation in mitochondrial ATP6 gene (m.9191T>C), that converts a highly conserved leucine residue into proline in human ATP synthase subunit a (aL222P), severely compromises the assembly of yeast ATP synthase and reduces by 90% the rate of mitochondrial ATP synthesis. Herein, we report the isolation of intragenic suppressors of this mutation. In light of recently described high resolution structures of ATP synthase, the results indicate that the m.9191T>C mutation disrupts a four α-helix bundle in subunit a and that the leucine residue it targets indirectly optimizes proton conduction through the membrane domain of ATP synthase

Efecto del medio de enraizamiento, número de hojas por estaca y lesionado de las estacas de Ixora Enana (Ixora coccinea L.) con Hormojardín Nro 4 | Effect of rooting media, leaves by cuttings and cutting wounding on the cutting rooting of Ixora coccinea L. treated with Hormojardin Nro 4

Las plantas de ixora poseen flores muy vistosas y son muy comunes en avenidas, edificios y casas. El objetivo de estetrabajo fue evaluar el efecto del medio de enraizamiento, número de hojas por estaca y lesionado de las estacas sobre elenraizamiento de estacas de Ixora Enana tratadas con Hormojardín Nro 4. Se utilizaron estacas provenientes de plantas deixoras aparentemente sanas, las estacas se tomaron del ápice de las plantas y tenían un tamaño aproximado de 20 cm delargo y 4 a 5 mm de diámetro. El diseño estadístico utilizado fue el de parcelas divididas con tres repeticiones, la parcelaprincipal estuvo constituida por el medio de enraizamiento (agua y suelo), la subparcela por la longitud de la lesión en labase de la estaca (0, 2 y 4 cm) y la subsubparcela por el número de hojas en las estacas a enraizar (0, 8 16 hojas). A todas lasestacas se les aplicó el producto comercial en polvo Hormojardín Nro 4 (ácido-α-naftalenacético), la aplicación se realizó enlos primeros 4 cm de la base de las estacas. Se determinó el número de raíces producidas por estaca a los 49 días despuésde la siembra. En general, los mejores tratamientos fueron en agua con estacas con una lesión de 2 cm y con 8 hojas yestacas sin lesiones con 16 hojas, mientras que para el suelo los resultados no fueron satisfactorios, observándose un pobreenraizamiento.Palabras clave: Ixora coccinea, propagación, auxinas, enraizamiento.ABSTRACTThe plants of Ixora coccinea L. have beautiful flowers and they are very common in roads, buildings and houses. Theobjective of the present work was evaluate the effect of rooting media, number of leaves/cutting and cutting injury oncutting rooting of dwarf Ixora treated with Hormojardin Nro 4. A cuttings from apparently healthy plants were used, thecuttings were taken from the plant tips and were approximately 20 cm long and have a diameter of 4 or 5 mm. A split-splitplotdesign was used with three replications. The main plot was constituted for the rooting media (water and soil), thesubplot was lesion longitude at the cutting end (0, 2 and 4 cm) and the sub subplot was the number of leaves/cutting. Allcuttings were treated with Hormojardin Nro 4 (acid-α-naftalenacetic), the application was made in the first 4 cm at thecutting end. The number of roots/cutting at 49 days after sowing was counted. The best results were obtained for water asmedia with 2 cm-cutting lesion and 8 leaves/cutting and for cutting without a lesion and 16 leaves/cutting, while for the soilas a media, the results were not successful, producing a poor rooting.Key word: Ixora coccinea, propagation, auxins, rooting

Molecular basis of diseases caused by the mtDNA mutation m.8969G>A in the subunit a of ATP synthase

The ATP synthase which provides aerobic eukaryotes with ATP, organizes into a membrane-extrinsic catalytic domain, where ATP is generated, and a membrane-embedded FO domain that shuttles protons across the membrane. We previously identified a mutation in the mitochondrial MT-ATP6 gene (m.8969G>A) in a 14-year-old Chinese female who developed an isolated nephropathy followed by brain and muscle problems. This mutation replaces a highly conserved serine residue into asparagine at amino acid position 148 of the membrane-embedded subunit a of ATP synthase. We showed that an equivalent of this mutation in yeast (aS175N) prevents FO-mediated proton translocation. Herein we identified four first-site intragenic suppressors (aN175D, aN175K, aN175I, and aN175T), which, in light of a recently published atomic structure of yeast FO indicates that the detrimental consequences of the original mutation result from the establishment of hydrogen bonds between aN175 and a nearby glutamate residue (aE172) that was proposed to be critical for the exit of protons from the ATP synthase towards the mitochondrial matrix. Interestingly also, we found that the aS175N mutation can be suppressed by second-site suppressors (aP12S, aI171F, aI171N, aI239F, and aI200M), of which some are very distantly located (by 20-30 Å) from the original mutation. The possibility to compensate through long-range effects the aS175N mutation is an interesting observation that holds promise for the development of therapeutic molecules

Assembly-dependent translation of subunits 6 (Atp6) and 9 (Atp9) of ATP synthase in yeast mitochondria

The yeast mitochondrial ATP synthase is an assembly of 28 subunits of 17 types of which 3 (subunits 6, 8, and 9) are encoded by mitochondrial genes, while the 14 others have a nuclear genetic origin. Within the membrane domain (FO) of this enzyme, the subunit 6 and a ring of 10 identical subunits 9 transport protons across the mitochondrial inner membrane coupled to ATP synthesis in the extra-membrane structure (F1) of ATP synthase. As a result of their dual genetic origin, the ATP synthase subunits are synthesized in the cytosol and inside the mitochondrion. How they are produced in the proper stoichiometry from two different cellular compartments is still poorly understood. The experiments herein reported show that the rate of translation of the subunits 9 and 6 is enhanced in strains with mutations leading to specific defects in the assembly of these proteins. These translation modifications involve assembly intermediates interacting with subunits 6 and 9 within the final enzyme and cis-regulatory sequences that control gene expression in the organelle. In addition to enabling a balanced output of the ATP synthase subunits, these assembly-dependent feedback loops are presumably important to limit the accumulation of harmful assembly intermediates that have the potential to dissipate the mitochondrial membrane electrical potential and the main source of chemical energy of the cell

Structure of the ATP synthase catalytic complex (F(1)) from Escherichia coli in an autoinhibited conformation.

ATP synthase is a membrane-bound rotary motor enzyme that is critical for cellular energy metabolism in all kingdoms of life. Despite conservation of its basic structure and function, autoinhibition by one of its rotary stalk subunits occurs in bacteria and chloroplasts but not in mitochondria. The crystal structure of the ATP synthase catalytic complex (F(1)) from Escherichia coli described here reveals the structural basis for this inhibition. The C-terminal domain of subunit ɛ adopts a heretofore unknown, highly extended conformation that inserts deeply into the central cavity of the enzyme and engages both rotor and stator subunits in extensive contacts that are incompatible with functional rotation. As a result, the three catalytic subunits are stabilized in a set of conformations and rotational positions distinct from previous F(1) structures